The Orioles (10-8) jumped in front, 4-1, after three innings, as J.J. Hardy drove in two runs and Adam Jones homered. That was not enough to overcome Arrieta's complete lack of control.
Despite retiring the first six batters, Arrieta (1-1) surrendered five earned runs over four-plus innings. The right-hander's feast-or-famine outing included five walks, two hits and six strikeouts.
"I really feel like the Dodgers didn't beat us today. I beat us," Arrieta said. "I put us in a tough situation. Not giving up many hits at all, just making their job a lot easier by putting them on base for free."
Handing out free passes has been a trend over the 27-year-old's last three starts. Arrieta has allowed 14 walks over his last 14 innings, and his ERA ballooned to 6.63 on the season.
Inability to maintain focus when he encounters rough patches is part of Arrieta's issue.
"Emotions affect mechanics," Orioles manager Buck Showalter said. "Everybody wants to know whether those [struggles] are mechanical or are they something else. ... He got out of the one inning with only one run, but obviously he created a lot of his problems."
Baltimore generated some early offense against emergency Dodgers starter Stephen Fife, including three runs in the first inning. Over the last six frames against Fife and five relievers, the Orioles had only four hits -- including Chris Davis' one-out double in the eighth off Kenley Jansen, who then retired the next two batters.
J.P. Howell (1-0) picked up the win and Dodgers closer Brandon League pitched the ninth for his fifth save.
The loss prevented the Orioles from securing their first series sweep of the season, though they still took two of three from the Dodgers (8-10). Baltimore is 4-2 on its current nine-game homestand, which wraps up with a three-game set against the Toronto Blue Jays starting on Monday.
"We got the series, that's a positive," Jones said. "We wanted the sweep, we were just unable to get it. The Dodgers weren't just going to hand it over to us."
The Orioles learned three hours prior to first pitch that, rather than facing Chad Billingsley, they would matchup against Fife -- owner of five previous Major League starts. Baltimore greeted him with three runs in the first, starting with Nick Markakis' one-out RBI single.
After the O's worked the bases loaded, Hardy knocked a two-out, two-run single into right for a 3-0 lead before the crowd of 41,265.
Jones' third-inning homer, his third of the season, put Baltimore in front, 4-1.
Fife threw 35 pitches in the first inning and lasted only 4 2/3 innings. Despite those struggles, he outlasted Arrieta.
Arrieta walked three batters and gave up a hit in the third, but escaped with only one run scoring. He officially lost his way in the fifth. Following a walk, a hit batter and another walk, Mark Ellis' two-run single cut the lead to 4-3 and ended Arrieta's day.
"If you watch the first couple [of] innings, there's no reason why I'm not pitching in the eighth today," Arrieta said.
Reliever T.J. McFarland promptly gave up an RBI double to Adrian Gonzalez and an RBI single to Matt Kemp.
"We got a couple of big hits," said Kemp, who had six hits in the series. "Everybody did a good job today. We started out down a couple of runs, but we continued to grind."
A.J. Ellis' RBI single in the seventh off McFarland put the Dodgers up, 6-4.
After winning 10 games in 2011, Arrieta finished 3-9 last season. He's scuffling again early in 2013. Though he remains in the rotation for now, his time could be short. Fellow starter Steve Johnson is moving closer to a return from the disabled list, and Arrieta is not moving closer to the pitcher many projected he would become.
"I'm so close to being so good -- and everybody knows it," Arrieta said. "That's frustrating. It's not going to keep me down, it's not going to keep me from continuing to work at and get to where I want to go."